Molecular Soil Biology 2024, Vol.15, No.4, 183-192 http://bioscipublisher.com/index.php/msb 184 research directions. The goal is to contribute to the scientific community's understanding of the environmental impact of Bt, promote biosafety assessments, and inform sustainable agricultural practices involving Bt technology. 2 Mechanism of Bt Action in Agricultural Applications 2.1 Bt as a biopesticide: mode of action on insect pests Bacillus thuringiensis (Bt) produces insecticidal proteins, primarily Cry proteins, which are highly specific stomach poisons targeting insect pests. These proteins bind to receptors in the gut of susceptible insects, causing cell lysis and ultimately leading to the insect's death. Bt-based biopesticides have been widely used in agriculture due to their specificity and environmental safety compared to conventional chemical insecticides (Sanchis, 2011). The mode of action involves the ingestion of Bt spores or Cry proteins by the insect, followed by the activation of these proteins in the alkaline gut environment, leading to the formation of pores in the gut cells and causing septicemia (Hilbeck et al., 2018). 2.2 Forms of Bt application: sprays vs. genetically modified (GM) Bt crops Bt can be applied in two primary forms: as microbial sprays or through genetically modified (GM) crops. Bt sprays involve the application of Bt spores and Cry proteins directly onto crops, providing immediate but short-term pest control due to environmental degradation factors such as UV light and rain (Sanchis, 2011). On the other hand, GM Bt crops are engineered to express Cry proteins throughout the plant tissues, offering continuous protection against pests. This method has been shown to reduce the reliance on chemical insecticides and improve pest management efficiency (Tabashnik et al., 2023). However, the persistence and potential ecological impacts of Cry proteins released from GM Bt crops into the soil through root exudates and plant residues are areas of ongoing research (Icoz and Stotzky, 2008; Li et al., 2022). 2.3 Persistence of Bt toxins in soil The persistence of Bt toxins in soil is influenced by both biotic and abiotic factors. Bt toxins can be released into the soil through root exudates, pollen, and decomposing plant residues from GM Bt crops (Li et al., 2022). The degradation of these toxins in soil is affected by microbial activity and physicochemical interactions with soil components. Studies have shown that Bt toxins can persist in soil for several months, with their persistence being soil-dependent and influenced by factors such as soil type, pH, and microbial activity (Icoz and Stotzky, 2008; Helassa et al., 2011). While some studies indicate that Bt toxins do not significantly alter soil microbial communities, the long-term ecological impacts require further investigation (O’Callaghan et al., 2005; Zhaolei et al., 2018). 3 Influence of Bt Applications on Soil Microbial Communities 3.1 Immediate effects on microbial diversity and composition The immediate effects of Bt applications on soil microbial communities have been a subject of extensive research. Studies have shown that the introduction of Bt crops, such as Bt maize, can lead to changes in the abundance of certain soil microorganisms. For instance, the presence of Bt traits in maize resulted in an increase in soil nematodes and protozoa (amoebae) (Griffiths et al., 2006). However, these changes were relatively minor compared to the effects of chemical insecticides. Another study found that the application of Cry1Ac protein, a common Bt toxin, did not significantly alter the diversity or population sizes of bacteria, fungi, and archaea in the soil over a 100-day period (Zhaolei et al., 2018). These findings suggest that while Bt applications can have immediate effects on specific microbial populations, the overall impact on microbial diversity and composition is limited. 3.2 Long-term impacts: shifts in microbial community structure Long-term studies on the impact of Bt crops on soil microbial communities indicate that there may be shifts in microbial community structure over time. For example, research on the long-term application of glyphosate, a common herbicide used in conjunction with Bt crops, showed an increase in the relative abundance of Proteobacteria and a decrease in Acidobacteria in the rhizosphere (Newman et al., 2016). This shift could have
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